A compact type printer of the electrophotographic method operating at low cost, accompanied with improved image performance via high resolution, has recently been desired. On the one hand, a toner having a small particle diameter has been utilized due to customer demand for the foregoing image quality.
In order to realize a compact printer at low cost, structure members of a developing apparatus and the apparatus configuration itself are to be simplified, or the number of parts are considered to be reduced. As a result, by an amount equivalent to the simplification of an apparatus, it was particularly difficult to adjust and control temperature and humidity, and process correction. Similarly to a toner transport system and a toner supply system, a toner itself was also desired to be improved in order to transport a toner smoothly.
When a toner having a small particle diameter is used for an apparatus, and the toner remains unused for a couple of days with no operation of the apparatus, the interparticle density is increased, whereby the fluidity tends to be markedly lowered, which is also called “packing”.
A technique to counter the above problem is to provide external additives, for which acicular titanium and titanium-enclosing silica are used as a method of improving toner transportability (refer to Patent Document 1, for example).
It is also reported that a toner into which such external additives are added exhibits excellent image transfer and image improvement (refer to Patent Document 2, for example).
However, these external additives are easily influenced by the image forming environment, and variation in charging tends to be dependent on the environment such as temperature and humidity, whereby variation in image density depending on the image forming environment has been unavoidable. Accordingly, application to the above printer accompanied with the simplified apparatus configuration was considered to be extremely difficult.
As described before, since the above printer is usually used at home or in small offices, in such the environment the printer tends to be left with no operation for a long time. Accordingly, when the printer is used after a long interval, toner transportability is seriously lowered, whereby problems such as appearance of a low density image caused by no predetermined amount of toner supplied to a developing portion, and the like have easily been produced.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 6-208241
(Patent Document 2) Japanese Patent O.P.I. Publication No. 8-44103